Operations, such as surveying, drilling, wireline testing, completions, production, planning and field analysis, are typically performed to locate and gather valuable downhole fluids. Surveys are often performed using acquisition methodologies, such as seismic scanners or surveyors to generate maps of underground formations. These formations are often analyzed to determine the presence of subterranean assets, such as valuable fluids or minerals, or to determine if the formations have characteristics suitable for storing fluids. Although the subterranean assets are not limited to hydrocarbon such as oil, throughout this document, the terms “oilfield” and “oilfield operation” may be used interchangeably with the terms “field” and “field operation” to refer to a field having any types of valuable fluids or minerals and field operations relating to any of such subterranean assets.
During drilling and production operations, data is typically collected for analysis and/or monitoring of the operations. Such data may include, for instance, information regarding subterranean formations, equipment, and historical and/or other data.
Data concerning the subterranean formation is collected using a variety of sources. Such formation data may be static or dynamic. Static data relates to, for instance, formation structure and geological stratigraphy that define geological structures of the subterranean formation. Dynamic data relates to, for instance, fluids flowing through the geologic structures of the subterranean formation over time. Such static and/or dynamic data may be collected to learn more about the formations and the valuable assets contained therein.
Reservoir characterization and asset management require information about formation fluids, reservoir pressure, and flow capacity. Obtaining this information at all stages of the exploration and development cycle is essential for field planning and operation. Understanding vertical flow behavior is also critical for proper reservoir management, especially at the time when completion decisions are made. Wireline formation testing has become quite attractive in the industry as a means to obtain the production potential of the formation before completing the well. Wireline formation testing tools may be used for many formation evaluation objectives, such as pressure profiling, sampling/fluid identification, interval pressure transient testing, and in-situ stress testing.
Permeability is a relevant parameter for managing a reservoir and adjusting well performance. Due to permeability's effect on reservoir displacement processes, the determination of permeability and permeability anisotropy (the ratio of vertical and horizontal permeability, kv/kh) is becoming increasingly important as emphasis shifts from primary to secondary and tertiary recovery.
Interval pressure transient testing (IPTT) along the wellbore using packer-probe formation testers provides dynamic permeability and anisotropy information with increased vertical resolution as compared to conventional well testing. During IPTT, the test tool is positioned at the interval to be tested and flow is induced from a dual packer tool module or from a sink probe while vertically displaced observation probes monitor the pressure response. The acquired flow and buildup transient data are used to obtain and analyze individual layer horizontal and vertical permeabilities. This testing technique yields formation properties well beyond the invaded zone, usually within “tens of feet” away from the wellbore in horizontal and vertical directions.
Appropriate thickness selection is important in nonlinear regression analysis for parameter estimation in determining horizontal and vertical permeability based on IPTT. However, building a layer cake model is not a trivial process even if high-resolution image-log data is available. Selecting the correct thickness of a formation in IPTT is significantly different as compared to a conventional transient test, where it is generally assumed that thickness is equal to the thickness of the perforated interval. There can be several flow units across the formation and it is not easy to select the correct thickness of the formation. However, if the IPTT is performed in a thick formation, the chance of seeing radial flow is low due to short duration nature of IPTT. In many cases, thickness information and radial flow data may not be available to determine horizontal and vertical permeability using traditional IPTT methods.